Us Weekly -- Bradley Cooper partied hard in two "Hangover" films -- something he was all too familiar with in his 20s.

Appearing on the cover of the Sept. 14 issue of The Hollywood Reporter, the "Words" actor, now 37, opens up about his decision to get sober at age 29. "I don't drink or do drugs at all anymore," the actor reveals. "Being sober helps a great deal."

At one of his lowest points, Cooper recalls, "I was at a party and deliberately bashed my head on the concrete floor -- like, 'Hey, look how tough I am!' And I came up, and blood dripped down. And then I did it again. I spent the night at St. Vincent's Hospital with a sock of ice, waiting for them to stitch me up."

Cooper attributes his problems with drugs and alcohol to feeling insecure as he struggled to kick-start his acting career. "I was so concerned what you thought of me, how I was coming across, how I would survive the day. I always felt like an outsider," he explains.

"I just lived in my head. I realized I wasn't going to live up to my potential, and that scared the hell out of me. I thought, 'Wow, I'm actually gonna ruin my life; I'm really gonna ruin it.'"

Though friends attempted to help Cooper realize he had a problem, "Part of me believed it, and part of me didn't," he tells The Hollywood Reporter. "But the proof was in the pudding: I'd always gotten up at the crack of dawn, and that was out the window. I remember looking at my life, my apartment, my dogs, and I thought, 'What's happening?'"